Field of the Invention
The present invention relates to a halogen-free reactive flame-retardant polyester, especially to a modified phosphorus-containing unsaturated polyester.
Descriptions of the Related Art
Flame retardants can be divided into three types: halogen-based flame retardants, silicon-based flame retardants and phosphorus-based flame retardants. Halogen-based flame retardants have been the most important type since the 20th century because of the good flame retardance, low utility level, low influence on material properties, and low price. However, the prospective of halogen-based flame retardants, especially in electronic/electrical industries, is not optimistic, because halogen pollutes the environment with a great amount of smoke and corrosive gases that are generated during thermolysis or combustion of the polymer materials using halogen-based flame retardants. Recently, phosphorus-based flame retardants have gradually taken the place of halogen-based flame retardants because they have less smoke, are non-toxic and have little or no halogen.
9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)
and its derivatives are newly developed phosphorus-based flame retardants over recent years. Due to the particular structures of DOPO molecules, DOPO not only has more excellent thermal stability and chemical stability than general ring-unformed organic phosphate, but includes the following advantageous characteristics: high carbon content, halogen-free, low smoke, non-toxic, no migration, lasting flame retardance, etc. For example, both U.S. Laid-open Publication No. 2009/0198011 and Chinese Patent No. 101525420 B disclose a flame retardant containing DOPO.
However, the above described polyester containing DOPO has poor compatibility with non-polar solvents or radiation-curable materials (e.g., vinyl-based material)/monomers (e.g., styrene). When applied on coating material, a compatibility problem will be encountered, and this will lead to an uneven distribution of the cured coating layer, precipitates of flame-retardant material etc, and thus limit its application.
In view of the above, the present invention provides a modified phosphorus-containing unsaturated polyester, which is radiation-curable and has good compatibility with and can be cross-linked with other radiation-curable materials (e.g., vinyl-based material). The polyester can also be easily synthesized and mass-produced. Furthermore, the use of the modified phosphorus-containing unsaturated polyester has become so widespread because it has good compatibility with non-polar solvents or monomers (e.g., styrene). The contractibility of the film prepared from the modified phosphorus-containing unsaturated polyester is low.